/errors/campaign_budget_error.proto

--- v20/errors/campaign_budget_error.proto  2025-08-05 14:39:40.000000000 +0000
+++ v21/errors/campaign_budget_error.proto  2025-08-05 14:39:46.000000000 +0000
@@ -98,5 +98,10 @@

     // Budget amount must be unset when BudgetPeriod is CUSTOM.
     BUDGET_AMOUNT_MUST_BE_UNSET_FOR_CUSTOM_BUDGET_PERIOD = 21;
+
+    // Budget amount or total amount must be above this campaign's per-day
+    // minimum. See the error's details.budget_per_day_minimum_error_details
+    // field for more information.
+    BUDGET_BELOW_PER_DAY_MINIMUM = 22;
   }
 }